Flying discs such as are used for sport and exercise have been known for many years, since first marketed by the Wham-O Mfg. Co., under the trademark FRISBEE.RTM. disc. More recently, a variety of flying discs have been introduced onto the market.
One recent design having a circular insert in the center of an annular disc is disclosed by DeWitt, U.S. Pat. No. 4,176,843. DeWitt provides for a thin circular insert to be attached to an annular flying disc by means of pins extending from the disc through holes in the insert. The pins are thermally deformed to retain the insert. The problem with DeWitt is that it is suitable only for attaching inserts of relatively undeformable material. This method is unsuitable for attachment of an insert comprising a thin film material such as a polyester sheet since the pegs could deform the sheet and ultimately slip through holes in the periphery of the insert. Alternative methods of bonding a central insert to an annular disc, suggested by DeWitt, include adhesives or thermoplastic bonding. Since the insert in DeWitt is composed of the same thermoplastic material as the annular disc, the two may be readily joined by these methods.
A method of attaching a circular insert of a plastic material such as polyester to an annular flying disc is disclosed in Harrington, U.S. Pat. No. 4,204,357. Harrington shows an annular disc having a plurality of projections molded near its inner perimeter. An insert with a plurality of holes adjacent to its perimeter fits over the disc and associated projections. The projections are heated and flattened out to hold the insert to the disc. Harrington also teaches the application of an adhesive tape over the heads of the projections to further hold the insert in place.
This method suffers several deficiencies for the attachment of a polyester insert. Without some positive means of attachment, the insert will detach from the disc, either by elastic deformation of the flattened projections or by deformation of the holes in the insert. The adhesive tape alone is ineffective to hold the insert to the disc.
Because of the diverse composition of polyester and a thermoplastic such as polyethylene, of which such discs are usually constructed, the polyester cannot be fusion bonded to a thermoplastic disc with any degree of success. The polyester may slowly detach from the annular section of the disc, impairing the disc's aerodynamic integrity, or may separate completely, defeating the purpose of the device and detracting from its aesthetic appeal.
Harrington recognizes this fact and teaches a rather long and complex method of bonding polyester to polyethylene using a flame to specially prepare the surface for a critically defined time period. A special adhesive must be applied to the surfaces to be bonded and allowed to cure before the surfaces are joined. This procedure practically requires that every disc be hand made.
The foregoing gives rise to the need for a practical method and structure for securing an insert of one material to a disc constructed of a different material.